Air-compressor piston



Dec, 30, 1924.

F. T. CABLE AIR COMPRESSOR FISTON Filed June 30 1920 2 Sheets-Sheet 1De@ 30, 19?-4. 1,520,852 F. T. CABLE A-IR COMPRESSOR PI STON Filed June30, 1920 2 Sheets-Sheet 2 TUE/wwf aw/vmware cao/er l, ATTORNEYS PatentedDec. 30, 1924,

UNI-rr: STATES PATENT' OFI-#leila FRANK TAYLOR CABLE, OF.; NEWHII'.|O1\TZDO1\T,V CONNECTICUT, `ASSllGrN'ORiTO ELECTRIC i BOAT COMPANY,A CORPORATION F NEW JERSEY.

` AIR-COMPRESSOR PISTON.

Application led June 30, 1920K.v Serial No. 393,066.

To ally whom t may concern.'

Be `it knownthatl, FRANKrT. CABLE, a citizen of the United States,residing at New London, in thelcountyof NewV London, State ofConnecticut, lhave invented certain new and useful Improvements inAir-Compressor Pistons; and I do hereby declare the following to be a.full, clear, andeXact description of the invention, such as will enableothers skilled in the art to which it appertains to make and use thesame. y

. This invention relates to two-stagel aircompressors, and moreparticularly to the second-stage'pistons used in such compressors. n y

According to the present practice the first and second stage pistons oftwo-stage air compressors are rigidly connected. .This

makes it necessary that the wallsof the first and second .stagecylinders be exactly parallel and-that the-two pistons be in perfectalignment. In practice Kthese conditions are difficult to meet,requiring as they do, exact and painstaking workmanship, and as a very rslight deviation from exact parallelism between the parts results in'rapid wear, particularly in the second stage cylinder, it has beenvfound diicult to maintain a tight fit between the-second-stage pistonand its cyl- 3U inder for more than short periods. The wea-r is taken upin llarge measure by the snap rings ofthe piston which must, inconsequence, be renewed, sometimes as often as every two or threemonths. This operation is ditlicult and costly as the compressor must beentirely dismantled and both pistons removed in order to gain access tothesecondstage piston.

It is, therefore, clear that could some means be. devised for minimizingthis wear and obviating the necessity for such frequent replacements ofthe second-stage piston rings, a very substantial saving in time andexpense could be effected. It is broadly an object of the inventiontoaccomplish this.

Going back to `first causes, the origin of the trouble isy found in thepractical difficulty of getting perfect alignment between the twocylinders which are preferabl yintegrally cast and must-be machined witmost exacting care. This difficulty has been overcome by thev present`invention through the simple expedient of doing away with the necessityfor such exact alignment. To do this'the two pistons are mounted forre1-ative, lateral and angular play, and thus automatically adjustthemselves to any i-naccuracies in the cylinder parallelism; -In doingthis two important results yare obtained; first, the wear `is minimized,and,

second, the need for scrupulous care in machining or grindingthe'cylinder bores is done away with. f However, aA certain amount o-fwear is inevitable, and as the' leakagearound the pistons incidentiuponthis wear yis more pronounced in the second-stage cylinder than in theirst,'ity still becomes necessary and desirable occasionally to removethe second` stage piston for the replacement of its snap rings or thesubstitution of a new piston. Accordingto the present invention meanshave been devised whereby this may be done by simply removing the secondstage head and without dismantling thel whole compressor. l l

It' has been found advantageous to eliminate pistonrings entirely onythe lsecondstage piston and to employ a soecalled solid piston havingconsiderablyl greater surface contact with the cylinder walls than is ordinarily the case, andpro-vided with a series of peripheral grooves vo-rseal rings, such grooves being old in this and analogous arts. As'thewear on such a piston and its cyl` inder cannot be compensatedfforvbytheuse of a new set of snap rings,nor Iyet by the substitution of a newpiston having the old original diameter, it becomes necessary to bushthe cylinder with aremovable bushing. The provision of .suchi a bushingis contemplated by the presentinvention.

i To recapitulate,.the objects of this invention'are: f'

To minimize wear in the second-stage cylinder and do away with the needfor nice alignmentY 'between thelirstf-and second stage, cylinders andpistons by mounting the two pistons for relative play: 1

To` provide meansfor withdrawing' the second-stage piston throughthefsecondestage hea-d and' without entailing adismantling ofthe'compressor; and

To providel the second-stage':cylinderf with a bushingfwhich shall beremovable in the same mannerthat thesecond-'stage piston is removable.`

A'still further object which shall be'm'ade clearer from the followingdescription is to'provide ay self-aligning second-stage piston whichshall have no mechanical connection with the first-stage piston, relyingupon air pressure to force it'down.

Other `and minor objects will be apparent as the description proceeds.

In order that the invention may be more cle-arly understood reference ishad to the accompanying drawings disclosing one speciiic embodimentthereof, although it is to be distinctly understood that the inventionin its broader aspects is not limited to these details of construction.

Fig. 1 is a vertical section through a. twostage air compressor showingthe construction of one form of second-stage piston made in accordancewith this invention and a part of the first-stage piston connectedthereto. As shown in this figure the second-stage head has been removedand the piston moved to a position in readiness for removal;

Fig. 2 is a vertical section of a modiiied form of second-stage pistondesigned to have no mechanical connection with the firststage piston;

Fig. 3 is a perspective view of the two-part collar used in forcing thebushing from its cylinder.

Fig. 4 is a vertical section through a twostage air compressor showingthe second stage piston of Fig. 2 mounted within the second stagecylinder.

In the drawings, 1 represents a two-stage air-compressor. In thiscompressor, 2 represents the first-stage cylinder, 3 the secondstagecylinder, 4 the first-stage. piston, and 5 the second-stage piston, thislast being provided with peripheral grooves 6 which fill with oil andserve as seal rings. The walls of the two cylinders are integrally castand form in effect one cylinder having bores of two different diameters.The two pistons are connected by means of a bolt 7 which passes throughthe upper end of piston 4, being keyed thereto at 8, and is provided atits upper end with a special nut 9 which bears upon an internal annularflange 10` situated near the upper end of piston 5. This nut is screwedupon threaded end 11 of bolt 7 and locked in posit-ion by means oftapered pin 12' which is screwed in the upper end of nut 9 and seated ina tapered and split socket 13 in the threaded end 11 of the bolt.Insertion of pin 12 into socket 13 expands threaded end 11 and fixes thenut 9 tightly in position. Piston 5 is provided at its upper end with asemi-spherical cap 14 locked in position by means of screw 15. Cylinder3 is bushed by means of a removable sleeve or bushing 16 forming thewearing surface for the piston 5.

Play between the two pistons is permitted by clearance spaces 17, 18 and19. In a case where alignment of the two cylinders hap-- pened to beparticularly bad, piston 5 might be twisted so far as to bind at thepoint where the edge of nut 9 bore upon flange 10. in order to preventthis the upper face. of this iiange is dished slightly as shown at 20.

To remove piston 5, the second-stage head is detached and the twopistons moved up to the position shown in Fig. 1. Cap 14 may then bereadily removed and then in succession pin 12 and nut 9. IVith this doneit becomes an easy matter to lift piston 5 from its cylinder with thehelp of a. special wrench having a pin which cooperates with a hole 21drilled in the side of the piston near its upper end.

To remove the bushing, the first-stage piston is drawn down below thelower end o of the bushing and the two-part collar 22 shown in Fig. 3introduced through cylinder 3 and seated upon the upper end of piston 4.An annular groove 23 is bored in the upper end of this piston and isadapted to receive aI depending flange 24 on collar 22. The diameter ofthis collar is greater than the internal diameter of the bushing butless than the external. Upon again moving the piston 4 upward theperipheral face of collar 22 will bear against the lower end of thebushing and force it out of its cylinder a short distance. It is then aneasy matter to complete the removal.

By making both the piston and its bushing removable, it becomes possibleto replace them with a new' pair which have been accurately fitted atthe factory. A tight lit is, therefore, assured. IVithout the provisionof a removable bushing it is a diHicult matter when replacing wornpistons of this type to attain a perfect iit for the obvious reason thatthere are no snap rings to take up the wear upon the cylinderwalls.

A modified form of second-stage piston is shown in Figs. 2 and 4, thenovelty of which resides in the fact that there is no mechanicalconnection whatever between it and the first-stage piston. This modifiedpiston comprises a cylindrical shell 25 provided with peripheral grooves26 which act as sealing rings as described before. A case-hardened cap27 incloses the lower end of the piston and is locked in place by meansof screw 28. This cap bears upon the upper end kof the first-stagepiston. In operation, the compression stroke of the first-stage pistonpushes the second-stage piston along its cylinder and thus effects thesecond compression. Upon the return stroke the air which has justpreviously been compressed in the first-stage cylinder and is under apressure of about seventyfive pounds per square inch is led into theupper end of the second-stage cylinder. This pressure is ample to forcethe looselyv mounted second-stage piston downward and keep cap 27 inconstant contact with the first-stage piston. This arrangement evensimpler than that shown in Fig. 1;

errors in alignment are automatically taken care of, and the removal ofthe piston is an easy mattei'.

Although this invention has been spoken of and described in connectionwith twostage air-compressors, it is obvious that the principlesinvolved might easily be applied to compressors operating in more thantwo stages. It is also obvious that the invention is not necessarilylimited to air-compressors, but is applicable to pumps or any othermachines which present similar problems in the matter of alignment andremoval of parts.

I claim:

l. In a two-stage air-compressor the comhination of first andsecond-stage pistons having no mechanical connection between them.

9,. In a two-stage air-compressor the combination of' first andsecond-stage cylinders and first and second-stage pistons in substantialalignment, mounted t-o reciprocate within their respective cylinders,and having no mechanical connection with each other, Contact betweenthem being maintained by the air pressure within the secondstagecylinder.

3. In a multi-stage air-compressor or the like, the combination of aplurality of cylinders of progressively increasing pressure, a pluralityof pistons in substantial alignment, mounted to reciprocate within theirrespective cylinders, and having no mechanical connection with oneanother, contact between adjacent pistons being maintained by the airpressure within the higher pressure cylinder.

4. A second-stage piston for air-compressors comprising the combinationof a cylindrical body portion and a cap at one end thereot4 adapted tobear upon the end of the first-stage piston.

5. In a two-stage air-compressor, the combination of first andsecond-stage cylinders, first and second-stage pistons in substantialalignment mounted to reciprocate within their respective cylinders, aremovable hea-d on the second-stage cylinder and means per' mittingseparation of the two pistons and removal of the second-stage pistonthrough the outer end of the second-stage cylinder.

6. In a two-stage air-compressor, the combination of first andsecond-stage cylinders, first and second-stage pistons in substantialalignment mounted to reciprocate within their respective cylinders, aremovable bushing or sleeve in the second-stage cylinder, a removablehead on the second-stage cylinder, and means for removing bothsecondstage piston and bushing through the Outer end of the second-stagecylinder.

7. In a two-stage air-compressor, the combination of' first andsecond-stage cylinders, first and second-stage pistons in substantialalignment mounted to reciprocate within their respective cylinders, aremovable bushing or sleeve in the second-stage cylinder, a removablehead on the second-stage cylinder, means for removing the second-stagepiston and means cooperating with the upper end of' the first-stagepiston to move the bushing out of its cylinder.

In testimony whereof I afx my signature.

FRANK TAYLOR CABLE.

